Cruciate-retaining knee prosthesis

ABSTRACT

Certain embodiments generally provide an improved tibial base member comprising keel portions that allow one or both cruciate ligaments to be preserved. Other embodiments provide improved lateral and/or medial inserts having a mesial lip that helps relieve and or prevent impingement between the femoral component and the tibial eminence. Other embodiments provide improved femoral components having various chamfers to provide additional clearance with respect to the tibial eminence and posterior cruciate ligament without decreasing bone coverage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/989,733, filed May 25, 2018, which is a divisional of U.S. patentapplication Ser. No. 14/556,623, filed Dec. 1, 2014, which is acontinuation of U.S. patent application Ser. No. 13/016,175, filed Jan.28, 2011, now U.S. Pat. No. 8,900,316, issued Dec. 2, 2014, which claimspriority from U.S. Provisional Application Ser. No. 61/372,556 filed onAug. 11, 2010, U.S. Provisional Application Ser. No. 61/382,287 filed onSep. 13, 2010, and U.S. Provisional Application Ser. No. 61/299,835filed on Jan. 29, 2010. The contents of the prior applications arehereby incorporated by reference.

RELATED FIELDS

Prostheses for use in knee arthroplasty, such as tibial and/or femoralimplants, which may in some instances facilitate the retention of one orboth cruciate ligaments.

BACKGROUND

In total knee arthroplasty, the convention is to resect the entireproximal tibia to create a plateau surface on which a tibial baseprosthesis can be implanted. Such conventional resection techniquestypically sacrifice one or both of the anterior cruciate ligament (ACL)and the posterior cruciate ligament (PCL) since the resections removedthe bony attachment site for those ligaments (the “tibial eminence”).Often, PCL and ACL functions are replaced by the prosthesis, which mayutilize a stabilizing post on the tibial insert, and a correspondingreceptacle on the femoral component or increased sagittal conformity.While these prostheses generally restore anterior-posterior stability,they may not feel as “natural” as a normal knee and are lesstissue-conserving.

If any one or both of the cruciate ligaments are salvageable, it issometimes desirable (especially for young and active patients) toconserve either or both the ACL and PCL in order to preserve naturalbiomechanics, range of motion, and feeling.

In current PCL-sparing knee implants, a posterior portion of the tibialinsert and/or tibial base member may have a slight cut-out to providespace for the PCL and its attachment site on a remaining portion of thetibial eminence. A surgeon must remain careful not to resect portions ofbone adjacent the PCL attachment areas. The ACL is generally sacrificedwhen using these so-called posterior cruciate-retaining prostheses.

Alternatively, a surgeon may attempt to preserve both the ACL and PCL,which is sometimes accomplished by installing two unicondylar implants.The tibial eminence and cruciate ligaments attached thereto are leftintact. The medial and lateral tibial plateau areas are resected andreplaced with separate unicondylar tibial trays and correspondinginserts. One disadvantage of implanting two separate unicondylarimplants includes the difficulty in properly aligning the two implantsin relation to each other. If the two implants are not aligned properly,wear may be accelerated, mechanical axis alignment may be compromised,and femoral motion may feel unnatural to the patient. Surgicalimplantation time may also be increased due to the added complexity ofinstalling two implants instead of one.

In lieu of two separate unicondylar implants, surgeons have thealternative option of preserving both the ACL and PCL by implanting asingle bi-cruciate retaining implant, which comprises a single tibialbearing member (which may be an insert) and/or tibial base member. Priorart bi-cruciate retaining implants are essentially formed of an insertand a base member, each having two unicondylar portions joined by a thinanterior bridge which connects the two. The thin anterior bridges mayfail to support the high torsional loading experienced by activepatients, and past implants have been known to eventually bend or shearin half over time, requiring premature revision surgery. Even minorbending and shearing experienced by such prior art devices may reduceperformance and eventually cause loosening or de-laminating of theimplant from the bone an either or both of the medial and lateral sides.

Additional problems with prior bi-cruciate retaining deigns includefracture of the bone adjacent to the area connecting the ACL to thetibia (i.e., the anterior tibial eminence). Such fractures areespecially common when bone portions anterior to the ACL attachmentpoint are removed in order to provide enough space for the medial andlateral side portions to be connected by said thin anterior bridge.

SUMMARY

When compared to prior art designs, at least some of the embodiments ofthe cruciate-retaining tibial prostheses described herein providegreater rigidity, torsional and bending stiffness, and resistance totorsional flexing, bending, and/or shearing between medial and lateraltibial portions.

These and other embodiments provide additionally or alternatively atibial prosthesis for at least partially replacing a proximal portion ofa tibia, the tibial prosthesis comprising an inferior surface contactwith a resected surface on the proximal portion of the tibia, and a keelfor penetration into a cavity formed in the proximal tibia, wherein thekeel extends at an inferior-posterior angle away from the inferiorsurface, wherein the tibial prosthesis defines a central notch extendingbetween, the medial and lateral baseplate portions posterior to theconnecting baseplate portion, wherein the central notch has a sufficientwidth and length to receive a portion of a tibial eminence including ananterior cruciate ligament attachment site and a posterior cruciateligament attachment site, and wherein the central notch comprises amedial edge and a lateral edge, wherein an angle defined by the medialedge and a base of the anterior keel portion is acute, and wherein anangle defined by the lateral edge and the base of the anterior keelportion is obtuse.

Also disclosed are tibial prostheses wherein a posterior face of theanterior keel portion is offset from a posterior face of the connectingbaseplate portion.

Also disclosed are tibial prostheses wherein a superior surface of thetibial prosthesis includes at least one lock member for securing atibial insert.

Also disclosed are tibial prostheses wherein a superior surface of thetibial prosthesis includes at least two lock members for securing amedial tibial insert and a lateral tibial insert.

Also disclosed are tibial prostheses for at least partially replacing aproximal portion of a tibia, the tibial prosthesis comprising a medialbaseplate portion, the medial baseplate portion having a medial inferiorsurface for contact with a medial resected surface on the proximalportion of the tibia, a lateral baseplate portion, the lateral baseplateportion having an lateral interior surface for contact with a lateralresected surface on the proximal portion of the tibia, a connectingbaseplate portion extending between the medial and lateral baseplateportions, wherein the tibial prosthesis is asymmetric about a midlineextending in an anterior-posterior direction between the medial andlateral baseplate portions and the medial baseplate portion extendsfurther anteriorly than the lateral baseplate portion.

Also disclosed are tibial prostheses wherein an area defined by themedial baseplate portion in a transverse plane is greater than an areadefined by the lateral baseplate portion in the transverse plane.

Also disclosed are tibial prostheses wherein the tibial prosthesis is abicruciate-retaining tibial prosthesis.

Also disclosed are tibial prostheses wherein the tibial prosthesisdefines a notch extending in a generally anterior-posterior directionbetween the medial and lateral baseplate portions and is positionedposterior to the connecting baseplate portion; and wherein the notch isof sufficient length to receive as least a portion of an eminence of thetibia including an anterior cruciate ligament attachment site and aposterior cruciate ligament attachment site.

Also disclosed are tibial prostheses wherein the notch comprises amedial edge, a lateral edge, and an anterior edge, herein an angledefined by the medial and anterior edges is acute, and wherein an angledefined by the lateral and anterior edges is obtuse.

Also disclosed is a tibial prosthesis for at least partially replacing aproximal portion of a tibia, the tibial prosthesis comprising a medialbaseplate portion comprising a medial inferior surface for contact witha medial resected surface on the proximal portion of the tibia, alateral baseplate portion comprising a lateral inferior surface forcontact with a lateral resected surface on the proximal portion of thetibia, a connection baseplate portion extending between the medial andlateral baseplate portions, the connection baseplate portion comprises aconnection inferior surface, a keel for penetration into a cavity formedin the proximal tibia, wherein the keel extends at an inferior-posteriorangle away from at least one of the medial inferior surface, the lateralinferior surface, and the connection inferior surface.

Also disclosed are tibial, prostheses wherein the keel includes ananterior keel portion, a medial, keel portion, extending from the medialinferior surface, and a lateral keel, portion extending from the lateralinferior surface, wherein the anterior keel portion extends at theinferior-posterior angle away from the connection inferior surface.

Also disclosed are tibial prostheses wherein at least a part of theanterior keel portion extends in a generally medial-lateral direction onthe connection baseplate portion, wherein at least a part of the medialkeel portion extends in a generally anterior-posterior direction of themedial baseplate portion, and wherein at least a part of the lateralkeel portion extends in a generally anterior-posterior direction on thelateral baseplate portion.

Also disclosed are tibial prostheses wherein the anterior keel portionjoins the medial and lateral keel portions at areas of increasedthickness.

Also disclosed are tibial prostheses wherein the anterior keel portionjoins the medial and lateral keel portions at areas of increased width.

Also disclosed are tibial prostheses wherein the connection baseplateportion increases in thickness in an anterior posterior direction.

Also disclosed are tibial prostheses wherein the medial and lateral keelportions decrease in height as the medial and lateral keel portionsextend in an anterior to posterior direction.

Also disclosed are tibial prostheses wherein the anterior keel portionextends across the connection baseplate portion in an anterior-medial toa posterior-lateral direction.

Also disclosed are tibial prostheses wherein a posterior face of theanterior keel portion is offset from a posterior face of the connectionbaseplate portion.

Also disclosed are tibial prostheses wherein the tibial prosthesisdefines a central notch extending between the medial and lateralbaseplate: portions: posterior to the connection baseplate portion,wherein, the central notch, has a sufficient width, and length toreceive a portion of a tibial eminence including an anterior cruciateligament attachment site and a posterior cruciate ligament attachmentsite.

Also disclosed are tibial prostheses wherein the central notch comprisesa medial edge and a lateral edge, wherein an angle defined by the medialedge and a base of the anterior keel portion is acute; and wherein anangle defined by the lateral edge and the base of the anterior keelportion is obtuse.

Also disclosed are tibial prostheses wherein the tibial prosthesis isasymmetric about a midline extending in an anterior-posterior directionbetween the medial and lateral baseplate portions and the medialbaseplate portion extends further anteriorly than the lateral baseplateportion.

These or other embodiments provide additionally or alternatively atibial prosthesis for at least partially replacing a proximal portion ofa tibia, comprising a tibial articulation surface for articulation witha femoral condylar articulation surface, wherein the tibial articulationsurface defines a mesial lip extending in an anterior to posteriordirection along a mesial edge of the articulation surface; where in themesial lip is raised by a height relative to a corresponding centralportion of the articulation surface; and wherein the height with whichthe mesial lip is raised relative to the corresponding central portiondecreases in an anterior to posterior direction.

Also disclosed are tibial prostheses wherein the tibial articulationsurface is a medial tibial articulation surface and wherein at least aportion of the medial tibial articulation surface is concave in asagittal plane.

Also disclosed are tibial prostheses wherein an anterior-mesial portionof the medial tibial articulation surface is curved to at leastpartially conform to the femoral condylar articular surface.

Also disclosed are tibial prostheses wherein a posterior-outer portion,of the medial tibial articulation surface is substantially flat and doesnot substantially conform to the femoral condylar articular surface.

Also disclosed are tibial prostheses wherein the tibial articulationsurface is a lateral tibial articulation surface; and wherein thelateral tibial articulation surface is convex in a sagittal plane.

Also disclosed are tibial prostheses wherein an anterior-mesial portionof the lateral tibial articulation surface is curved to at leastpartially conform to the femoral condylar articular surface.

Also disclosed are tibial prostheses wherein a posterior-outer portionof the lateral tibial articulation surface is substantially flat anddoes not substantially conform to the femoral condylar articularsurface.

Also disclosed are tibial prostheses wherein the tibial prosthesis is atibial insert; and wherein the tibial insert further comprises aninferior surface that includes at least one lock member for securing toa tibial baseplate.

Also disclosed is a tibial prosthesis for at least partially replacing aproximal portion of a tibia, comprising a tibial articulation surfacefor articulation with a femoral condylar articulation surface, whereinthe tibial articulation surface defines a mesial lip extending in ananterior to posterior direction along a mesial edge of the articulationsurface, wherein the mesial lip is raised by a height relative to acorresponding central portion of the articulation surface, and thereinan anterior-mesial portion of the medial tibial articulation surface iscurved to at least partially conform to the femoral condylar articularsurface, and wherein a posterior-outer portion of the medial tibialarticulation surface is substantially flat and does not substantiallyconform to the femoral condylar articular surface.

Also disclosed is a tibial prosthesis for at least partially replacing aproximal portion of a tibia, comprising: a tibial articulation surfacefor articulation with a femoral condylar articulation surface, whereinan anterior-medial portion of the tibial articulation surface at leastpartially conforms to the femoral condylar articulation surface and aposterior-outer portion of the tibial articulation surface does notsubstantially conform to the femoral condylar articulation surface.

Also disclosed are tibial prostheses wherein the anterior-mesial portionis curved to at least partially conform to the femoral condylararticulation surface.

Also disclosed are tibial, prostheses wherein the posterior-outerportion, is substantially flat such that the posterior-outer portiondoes not substantially conform to the femoral condylar articulationsurface.

Also disclosed are tibial prostheses wherein the tibial articulationsurface is a medial tibial articulation surface; and wherein the medialtibial articulation surface is concave in a sagittal plane.

Also disclosed are tibial prostheses, wherein the tibial articulationsurface is a lateral tibial articulation surface; and wherein thelateral tibial articulation surface is convex in a sagittal plane.

According to other embodiments, a tibial prosthesis for at leastpartially replacing a proximal portion of a tibia is also provided, thetibial prosthesis comprising, a tibial articulation surface forarticulation with a femoral condylar articulation surface, wherein thetibial articulation surface defines a mesial lip extending in ananterior to posterior direction along a mesial edge of the articulationsurface, wherein the mesial lip is raised a height relative to acorresponding, central portion of the articulation surface, wherein theheight with which the mesial lip is raised relative to the correspondingcentral portion decreases in an anterior to posterior direction, ananterior-mesial portion, of the tibial articulation surface at leastpartially conforms to the femoral condylar articulation surface and aposterior-outer portion of the tibial articulation surface does notsubstantially conform to the femoral condylar articulation surface.

Also disclosed are tibial prostheses wherein the anterior-mesial portionis curved to at least partially conform to the femoral condylararticulation surface.

Also disclosed are tibial prostheses wherein the posterior-outer portionis substantially flat such that the posterior-outer portion does notsubstantially conform to the femoral condylar articulation surface.

Also disclosed tibial prostheses further comprising at least one tibialarticulation surface for articulation with a femoral condylararticulation surface of a femoral component, wherein the femoralcomponent comprises a medial condyle and a lateral condyle and whereinat least one of the medial condyle and the lateral condyle comprises aposterolateral chamfer.

Also disclosed are tibial prostheses wherein the at least one tibialarticulation surface generally slopes in an anterior-posteriordirection.

Also disclosed are tibial prostheses wherein the at least one tibialarticulation surface comprises a medial articulation surface and alateral articulation surface, and wherein a slope of the medialarticulation surface in the anterior-posterior direction is differentfrom a slope of the lateral articulation surface in theanterior-posterior direction.

Also disclosed are tibial prostheses wherein the medial articulationsurface is associated with a medial insert and the lateral articulationsurface is associated with a lateral insert, wherein a thickness of themedial insert at an anterior portion, of the medial insert is differentthan a thickness of the lateral insert at a posterior portion of thelateral insert.

Also disclosed are tibial prostheses wherein the thickness of the medialinsert at the anterior portion of the medial insert is greater than thethickness of the medial, insert at a posterior portion of the medialinsert.

Also disclosed are tibial prostheses wherein a thickness of the medialinsert at a posterior portion of the medial insert is different than athickness of the lateral insert at a posterior portion of the lateralinsert.

Also disclosed are tibial prostheses wherein the thickness of thelateral insert at the anterior portion of the lateral insert is greaterthan the thickness of the lateral insert at a posterior portion of thelateral insert.

Also disclosed are tibial prostheses wherein the at least one tibialarticulation surface generally slopes in a medial-lateral direction.

Also disclosed are tibial prostheses wherein the at least one tibialarticulation surface comprises a medial articulation surface and alateral articulation surface, and wherein a slope of the medialarticulation surface in the medial-lateral direction is different from aslope of the lateral articulation surface in the medial-lateraldirection.

Also disclosed are tibial prostheses wherein the medial articulationsurface is associated with a medial insert and the lateral articulationsurface is associated with a lateral insert, wherein a thickness of themedial insert at an anterior portion of the medial insert is greaterthan a thickness of the lateral insert at an anterior portion of thelateral insert, and wherein the thickness of the medial insert at aposterior portion of the medial insert is different than the thicknessof the lateral insert at a posterior portion of the lateral insert.

Also disclosed are tibial prostheses wherein the anterior keel portionis positioned anteriorly on the connection inferior surface to engageanterior cortical bone when implanted in a patient.

Also disclosed are femoral components having various chamfers to provideadditional clearance with respect to the tibial eminence and PCL withoutdecreasing bone coverage. In some embodiments, the medial and/or lateralcondyles of the femoral component comprise a posterolateral chamfer. Insome embodiments, an anterior flange of the femoral component maycomprise an anterolateral chamfer on the lateral and/or medial sides.

Also disclosed are tibial prostheses further comprising at least onetibial articulation surface for articulation with a femoral condylararticulation surface of a femoral component, wherein the femoralcomponent comprises a medial condyle and a lateral condyle and whereinat least one of the medial condyle and the lateral condyle comprises aposterolateral chamfer.

Further areas of applicability will become apparent from the detaileddescription provided hereinafter. It should be understood that thedetailed description and specific examples, while indicating certainembodiments of the invention, are intended for purposes of illustrationonly and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate embodiments of the invention and togetherwith the written description serve to explain the principles,characteristics, and features of the embodiments. It should be notedthat while most or all of the drawings contained herein generallyillustrate implants configured for use with a patient's left knee,mirrored implants for use with a patient's right knee and symmetricallyconfigured implants for use with both left and right knees are alsoenvisaged. In the drawings:

FIGS. 1-3 are bottom isometric views of a tibial base member accordingto a first embodiment that employs one or more: bone ingrowth or cementmantle structures and a plurality of keel portions.

FIGS. 4-7 illustrate a tibial base member according to a secondembodiment that includes an underside recess for receiving a cementmantle.

FIGS. 8-11 illustrate a tibial base member according to a thirdembodiment.

FIGS. 12-15 Illustrate a tibial base member according to a fourthembodiment.

FIGS. 16-19 illustrate a tibial base member according to a fifthembodiment.

FIGS. 20-23 illustrate a tibial base member according to a sixthembodiment.

FIGS. 24-29 illustrate a tibial base member according to a seventhembodiment. the base member having an anterior wall portion configuredto contact an external portion of cortical bone adjacent to the anteriorcortex of the tibia.

FIGS. 30-35 and 47 illustrate a tibial base member according to aneighth embodiment, the tibial base member having three keel portions.

FIGS. 36 and 37 illustrate a tibial base member according to a ninthembodiment, which includes steps, textures, or jagged features presidedon the keel portions.

FIGS. 38-46 illustrate the tibial base member of FIGS. 30-35, and 47,shown assembled with medial and lateral articulating tibial inserts.

FIG. 48 illustrates a step of assembling the bicruciate-retaining tibialprosthesis shown in FIGS. 38-46.

FIGS. 49-52 are frontal coronal cross-sectional views schematicallyillustrating mating geometries between, a tibial base member and atibial eminence according to various embodiments.

FIG. 53 is a frontal coronal view of a bicruciate-retaining tibialprosthesis shown implanted on a proximal tibia.

FIGS. 54 and 55 illustrate posterior views of a lateral tibial insert.

FIG. 56 illustrates a lateral sagittal view of the lateral insert ofFIGS. 54 and 55.

FIG. 57 shows a coronal cross-sectional of the lateral insert of FIGS.54-56 when viewed from the anterior side.

FIG. 58 shows a sagittal cross-sectional view of the lateral insert whenviewed from the lateral side.

FIGS. 59 and 61 are posterior views of a medial tibial insert.

FIG. 60 is a medial sagittal view of the medial insert of FIGS. 59 and61.

FIG. 62 shows a coronal cross-sectional view of the medial insert whenviewed from the anterior side.

FIG. 63 shows a sagittal transverse cross-sectional view of the medialinsert when viewed from the medial side.

FIGS. 64-66 graphically illustrate the kinematics of one embodiment of afemoral implant when used in conjunction with the bicruciate-retainingtibial prostheses shown in FIGS. 38-46.

FIGS. 67a-67q illustrate the kinematics of FIGS. 64-66 for variousangles of flexion.

FIG. 68 is an anterior view of one embodiment of a bicruciate-retainingknee prosthesis (ACL and PCL sparing).

FIG. 69 is an anterior view of one embodiment of a cruciate-retainingknee prosthesis (PCL sparing).

FIGS. 70 and 71 are anteromedial views of the bicruciate-retaining andcruciate-retaining knee prostheses of FIGS. 68 and 69, respectively.

FIGS. 72 and 73 are posteromedial views of the bicruciate-retaining andcruciate-retaining knee prostheses of FIGS. 68 and 69, respectively.

FIGS. 74 and 75 are posterior views of the bicruciate-retaining andcruciate-retaining knee prostheses of FIGS. 68 and 69, respectively,showing optional clearance channels provided to the femoral component.

FIG. 76 is a superior view of a medial femoral condyle illustrating inparted cross-section an optional posterolateral chamfer according tosome embodiments.

FIGS. 77 and 78 are lateral sagittal views of the bicruciate-retainingand cruciate-retaining knee prostheses of FIGS. 68 and 69, respectively.

FIGS. 79 and 80 are posterolateral views of the bicruciate-retaining andcruciate-retaining knee prostheses of FIGS. 68 and 69, respectively.

FIG. 81 is a superior view of the femoral component shown in FIGS. 67a-80.

FIGS. 82-84 show various prospective views of the medial and lateralinserts of FIGS. 54-63.

FIG. 85 shows a bicompartmental knee implant according to anotherembodiment that employs a medial insert according to some embodimentsand that may be used in conjunction with a medial unicondylar tibialbase member (not shown) and that alternatively may be configured as alateral bicompartmental knee implant (not shown).

FIG. 86 shows a medial unicondylar knee implant according to anotherembodiment, which employs a medial insert according to some embodimentsand which may be used in conjunction with a medial unicondylar tibialbase member (not shown).

FIG. 87 shows a lateral unicondylar knee implant according to anotherembodiment, which employs a lateral insert according to some embodimentsand which may be used in conjunction with a lateral unicondylar tibialbase member (not shown).

FIG. 88 shows a monolithic bicruciate-retaining prosthesis according toone embodiment, wherein the tibial base member comprisesintegrally-formed articulating surfaces.

FIG. 89 shows a monolithic bicruciate-retaining prosthesis according toone embodiment, wherein the tibial base member is a fully or partiallyporous augment comprising integrally-formed articulating surfaces.

FIGS. 90a-90e show various sagittal cross-sectional views of lateralinsert when viewed from the medial side.

FIGS. 91a-91k show various coronal cross-sectional views of a lateralinsert when viewed from the posterior side.

FIGS. 92a-92e show various sagittal cross-sectional views of a medialinsert when viewed from the lateral side.

FIGS. 93a-93m show various coronal cross-sectional views of a medialinsert when viewed from the posterior side.

FIG. 94 is a medial sagittal view of a femoral component according toone embodiment.

FIGS. 95a-95k are various coronal cross sectional views taken along thelines A-A through K-K, respectively, of FIG. 94.

FIG. 96 is a perspective view of a resected tibia prepared to receivethe tibial base member of FIGS. 30-35 and 47.

FIGS. 97-98 are bottom isometric views of a tibial base member accordingto a tenth embodiment that includes one or more pegs.

FIG. 99 is a sagittal cross-sectional view of a lateral insert accordingto an embodiment.

FIG. 100 is a sagittal cross-sectional view of medial insert accordingto an embodiment.

DETAILED DESCRIPTION

The following description is merely exemplary in nature of certainselected embodiments and is in no way intended to limit the invention,its application, or uses.

1. Tibial Base Members

FIGS. 1-46 and 97-98 show various, non-limiting embodiments of tibialbase members, some of the features of which are discussed below.

FIGS. 1-3 show the underside of a first embodiment of a tibial basemember. Generally, base member 10 includes a medial portion 12 a, alateral portion 12 b, and a connecting portion 12 c. In this particularembodiment, the base member 10 has an asymmetric shape in some aspect.For instance, as shown in FIG. 3, the medial portion 12 a is larger thanthe lateral portion 12 b and aspects of the medial portion 12 a extendfurther anteriorly relative to lateral portion 12 b. In otherembodiments, the base member may reflect other asymmetries or may besymmetric.

The base member 10 of FIGS. 1-3 includes lips 15 a and 15 b defining acutout portion 8 between medial portion 12 a and lateral portion 12 b,which may provide clearance for a preserved tibial eminence, or portionsthereof. In the embodiment shown in FIGS. 1-3, the central cutoutportion 8 is approximately one-quarter to one-third of the tibialmedial-lateral width and thus configured to allow a majority of thetibial eminence to protrude through, although, in some embodiments, itmay be desirable to resect at least anterior portions of the eminence.For instance, in some embodiments, an anterior portion of the tibialeminence may be resected flush with the medial, and lateral tibial boneresections to provide space for the connecting portion 12 c. The amountof tibial bone removed to provide room for a connecting portion 12 cmay, in some embodiments, be in the range of ⅕ to ⅛ of the totalanterior-to-posterior dimension of the tibial eminence prior to bonepreparation. In this particular embodiment, the connecting portion 12 cis designed to preserve and protect bone around the ACL attachmentpoint, as well as eliminate stress-risers.

As shown, the central cutout portion 8 is generally centered in amedial-lateral direction of the tibial base member 10, which facilitatesmaintaining the medial/lateral widths of the medial 12 a and lateral 12b portions to be generally the same (and, in some embodiments, themedial lateral widths of inserts used in conjunction with the basemember 10). In other embodiments, it is not necessary for the medial 12a and lateral 12 b portions to be the same in medial/lateral dimensions.

The base member 10 shown in FIGS. 1-3 includes a keel extending distallytherefrom. In some embodiments, the keel may facilitate securing andretaining the base member to the patient's tibia. In some embodiments,the keel may add strength, torsional rigidity and stability to the basemember. In the particular embodiment shown, keel portions 14 a and 16 aextend from the medial portion 12 a of base member, keel portions 14 band 16 b extend from the lateral portion 12 b, and keel portion 14 cextends from the connecting portion 12 c.

In some embodiments, the keel portions may extend at an angle betweenapproximately 90 degrees and appropriately 45 degrees with respect tothe underside of the base member 10, although more or less pronouncedangles are also possible. In some embodiments, the keel portions mayextend distally at the same general angle or may extend at a differentangles with respect to one another. In some embodiment, the keelportions may be symmetric with respect to one another, or may beasymmetrically configured to suit bony anatomy or for other reasons.Other base member embodiments (discussed below) may have more or lesskeel portions than the base member 10 of FIGS. 1-3 and/or have keelportions of different configurations.

In the particular embodiment of FIGS. 1-3, and as shown best in FIG. 3,the anterior fin 14 c angles in a medial-lateral direction such thatmedial portions of the anterior fin 14 c are positioned furtheranteriorly than lateral portions. Anterior fin 14 c also slopes in atanterior/superior to posterior/inferior direction, some of the reasonsfor which are disclosed in connection with later embodiments describedherein. Anterior fin 16 c also includes a distal notch 13 (see FIG. 2)to optimize flexibility, reduce material, improve stress distribution,and/or provide additional rotational stability.

The base member of FIGS. 1-3 includes keel portions 16 a, 16 b extendingdistally from the medial 12 a and lateral 12 b portions of base member10, which, in some embodiments, may improve stability and/or rigidity ofthe base member 10 against forces that may be exerted thereon, such asforces having at least a component in an anterior and/or posteriordirection. Enhanced stability in the anterior-posterior direction may bedesirable in some, although not necessarily all, embodiments becausecertain femoral components (such as femoral component 400 shown in FIGS.67A-D) may, in some instances and uses, impart such forces on the tibialcomponents used therewith. In some embodiments, the insertion angle andpositioning of the one or more keel portions 16 a, 16 b may be optimizedin space for best fixation and best tibial fit, as well asanterior-posterior and rotational stability within the bone. Geometriesfor the keel portions 16 a, 16 b other than those shown explicitly inthe Figures are also contemplated.

Tibial base member 10 according to some embodiments may have surfacefinishes that are optimized for use with cemented or uncementedtechniques. In some embodiments, the base members have smooth orpolished surfaces, or may have a grit blasted surface finish, or otherrough surface finishes and textures such as ridges grooves, steps,flutes, spines, barbs, and combinations thereof. Bottom or distalsurfaces of medial portion 12 a and lateral portion 12 b may alsocomprise bone ingrowth structures such as a porous ingrowth surfaceswith or without hydroxyapatite. In some embodiments, one or more pocketsmay be provided on the distal or inferior undersurface of base member toaccommodate a cement mantle for cemented techniques. The one or morepockets may include means for increasing surface area of contact betweenthe implant and a cement mantle such as a waffle pattern, grooves,ridges, indentations, undercuts, porous portions, protrusions, or bumps15 c, which may be a porous metal material or surface-treated portion ofthe structure.

The keel portions 14 a, 14 b, 14 c, 16 a, and 16 b shown in FIGS. 1-3include outer face surfaces 14 a′, 14 b′, 14 c′, 16 a′, 16 b′respectively and inner face surfaces 14 a″, 14 b″, 14 c″, 16 a″, 16 b″respectively. In some embodiments, these face surfaces may containporous ingrowth surfaces, roughened surface treatments, hydroxyapatite,or biologies for improved fixation. In some embodiments, inner 14 a″, 14b″, 14 c″, 16″, 16 b″ and outer 14 a′, 14 b′, 14 c′, 16 a′, 16 b′ facesurfaces may be parallel to each other, or may extend at acute anglesrelative to each other. While shown to be generally planar, facesurfaces 14 a″, 14 b″, 14 c″, 16 a″, 16 b″, 14 a′, 14 b′, 14 c′, 16 a′,16 b′ of keel portion, 14 a, 14 b, 14 c, 16 a, and 16 b respectively maybe more complex B-spline or arcuate surfaces.

The base member 10 of FIGS. 1-3 includes blends or reinforcing members18 located between the anterior keel portion 14 c and the medial keelportion 14 a and the lateral keel portion 14 b, which may, in someembodiment, help to minimize the amount of bone removal necessary toaccommodate the implant. For instance, on the medial side, strategicblending of the reinforcing member 18 a helps keep the bottom edge ofthe keel portions away from cortical tibial bone. In this way,reinforcing members 18 form transitional areas between the anterior keelportion 14 c and the medial keel portion 14 a, and between the anteriorkeel portion 14 c and the lateral keel portion 14 b.

FIGS. 4-7 illustrate another embodiment of a tibial base member—basemember 20. Like the embodiment of FIGS. 1-3, tibial base member 20includes a medial portion 22 a from which a medial fin 24 a extends, alateral portion 22 b from which a lateral fin 24 b extends, and aconnection (or anterior) portion 22 c from which an anterior fin 24 cextends. Base member 20 may also comprise oblique medial fin 26 a andoblique lateral fin 26 b. Like the embodiment of FIGS. 1-3, anterior fin24 c may include a distal notch 23 (shown in FIG. 6), Superior surfacesof the base member 20 may comprise a medial locking portion 22 a′ andlateral locking portion 22 b″ in the form of recesses that areconfigured to receive medial and lateral inserts, respectively. Basemember 20 also includes medial bone contacting surface 22 a″ and lateralbone contacting surface 22 b″ for a cement mantle or which may be aporous ingrowth surface.

Reinforcement members 28 a, 28 b are generally cylindrical in shape tofacilitate bone preparation. For example, drills or small diameterreamers may be used to prepare the bone to accept the thicker regionthat form the intersections between the keel portions 24 a, 24 c, and 24b. Cylindrical and smooth arcuate shapes for the reinforcing member 28a, 28 b generally increase the strength at the corners of the cutoutbetween medial 24 a and lateral 24 b portions, which, in someembodiments, may be high stress areas.

FIGS. 8-11 illustrate a third embodiment, tibial base member 30, whichhas similar features as the base members 10 and 20 described above. Basemember 30 includes a medial eminence lip 39 a, a lateral eminence lip 39b, and an anterior eminence lip 39 c, shown in FIGS. 8 and 11, which maybe provided around the eminence cutout area to increase the overallstrength of the base member 30 along its inside edges. This addedstrength may be particularly important in some embodiments to resisttorsional or other forces exerted on the base member 30 when it isloaded posteriorly.

FIGS. 12-15 illustrate a fourth embodiment, base member 40, which hassimilar features as the base members described above with somevariations. As one example, as shown in FIG. 14, notch 43 is morepronounced. The configuration of reinforcing members 48 a, 48 b is alsodifferent, as reinforcing members 48 a, 48 b extend posteriorly and alsoextend further in a distal direction than the keel portions, such asmedial keel portion 44 a, as shown in FIG. 15.

FIGS. 16-19 illustrate a fifth embodiment, base member 50, which alsohas similar features as the base members described above with somevariations. As one example, as shown in FIG. 17, the reinforcing members58 a and 58 b are more pronounced. Moreover, as shown in FIG. 17,oblique fins 56 a and 56 b are positioned differently with respect tomedial and lateral portions 52 a, 52 b than in other embodiments.

FIGS. 20-23 illustrate a six embodiment, base member 60, which hassimilar features as the base members described above with somevariations. For instance, base member 60 includes a medial fin 64 a, ananterior fin 64 c, and a lateral fin 64 b, but does not include obliquefins. As shown in FIG. 22, anterior fin 64 c includes grooves or othersurface modifications. Base member 60 also includes an anterior eminencelip 69 c, which extends proximally from a superior van ace of the basemember (as shown in FIGS. 22-23).

FIGS. 24-29 illustrate a seventh embodiment, base member 70, which hassimilar features as the base members described above with somevariations. Base member 70 includes a medial fin 74 a, an anterior fin74 c, a lateral fin 74 b, and oblique fins 76 a, 76 b, which extend atan angle from medial and lateral fins 74 a, 74 b, respectively. Anteriorfin 74 c is positioned more anteriorly than in other embodiments, so asto engage anterior cortical bone on its inner surface 74 c″ and sit onan eternal cortical bone surface adjacent to the anterior cortex. Basemember 70 includes a medial eminence lip 79 a, a lateral eminence lip 79b, and an anterior eminence lip 79 c, shown in FIGS. 26 and 29, whichmay be provided along the medial and lateral sides of the eminencecutout area to increase the overall strength of the base member 70 alonginside edges.

FIGS. 30-35 and 47 illustrate an eighth embodiment, base member 80,having three keel portions—medial keel portion 84 a, anterior keelportion 84 c, and lateral keel portion 84 b FIG. 96 illustrates arejected tibia 220 prepared to receive the base member 80. As shown inFIG. 96, the tibial eminence 222 is intact. As shown in FIG. 35,anterior keel portion 84 c extends further distally than medial andlateral heel portions 84 a, 84 b, which, in some embodiments, mayenhance fixation. In addition, and as with some of the previousembodiments, anterior keel portion 84 c is angled and extends in asuperior-anterior to inferior-posterior direction (see FIG. 35) inrelation to the tibial resection plane and or the underside of anteriorportion 82 c, which may, in some embodiments facilitate increasing thedepth of the keel post ion for strength and ligation without adverselyinterfering with the anterior cortex of the tibia, and, in someembodiments, without requiring the connecting portion 82 c to be locatedso far posteriorly that it would interfere with the ACL attachment pointon the eminence. In some embodiments, the slope of the anterior keelportion 84 c helps prevent penetration of the anterior cortical bone ofthe proximal tibia, or splitting or cracking of the proximal tibiaduring insertion and impaction. In some embodiments, the slope of theanterior keel portion 84 c increases the amount of bone preservedbetween the anterior fin 84 c and the anterior tibial cortical bone inthis particular embodiment, the angle α between the inside surface 84 c″of the anterior keel portion 82 c and a bone contacting undersurface 82a″, 82 b″ of the base member 80 is between approximately 50 andapproximately 90 degrees, and more preferably between approximately 65and approximately 75 degrees, for example approximately 70 degrees. Insome embodiments, medial keel portion 84 a and lateral keel portion 84 balso extend at an inferior-posterior angle in some aspects, e.g. the topsurface of those keel portions.

As best shown in FIG. 35, in some embodiments, the posterior face of theanterior connecting portion 84 c (which is adjacent to lip 89 c) and theposterior side 84 c″ of the anterior keel portion 8 c may not inferredat the level of the proximal tibial resection plane, so as, in someembodiments, help to avoid weakening the anterior portion of the tibialeminence during the anterior keel portion preparation or cause fracture.In other words, the intersection of these two surfaces is offset apredetermined distance (r—shown in FIG. 35) to ensure that preparationof the bone for the anterior keel portion 82 c does not compromise thepreserved eminence.

As also shown in FIGS. 34 and 35, the angle θ between the lip 89 c ofthe anterior connecting portion 82 c and a bone contacting undersurface82 a″, 82 b″ of the base member 80. In this particular embodiment, isbetween approximately 60 and approximately 90 degrees, and morepreferably between approximately 82 and approximately 88 degrees, forexample approximately 85 degrees. This angle θ effectively creates anundercut to increase the amount of bone preserved at the anterior baseportion of a prepared anterior eminence and thereby reduces bonestresses. In other words, the anterior cut of the eminence is tapered insome embodiments such that the base area of the eminence is greater thanits proximal area. which improves the pull-off strength of the eminence222. The undercut formed by angle θ may also allow bone cement, putty,or other biologic materials to readily flow to the anterior base regionsof the eminence 222 thereby strengthening and filling in stress risersthat may be located at the corner of the base of the anterior eminencewhere the anterior eminence bone cut meets the proximal tibialresection. Material placed or packed into and around the undercut angleθ between the bone and the tibial base member 80 may also hold downportions of the bone once implanted, prevent micromotion of the tibialbase member 80, and avoid subsidence. As previously stated, theabovementioned angles and other geometric features may be altered tooptimally suit a patient's individual anatomy.

As best shown, in FIG. 30, the angle γ between the anterior fin 84 c andthe inside of the medial portion 82 a of this particular embodiment isbetween approximately 75 and approximately 90 degrees, and morepreferably between approximately 82 and approximately 88 degrees, forexample approximately 85.5 degrees. As best shown in FIG. 32, the angle.beta. between the anterior connecting portion 82 c and the inside ofthe lateral portion 82 b, in this particular embodiment, is betweenapproximately 90 and approximately 120 degrees, and more preferablybetween approximately 92 and approximately 98 degrees, for exampleapproximately 95 degrees. In other words, the anterior edge of thecutout portion between medial 82 a and lateral 82 b portions is angledsuch that the medial side of connecting portion 82 e lies moreanteriorly than the lateral side of the connecting portion 82 c. Theadditional anterior space on the anteromedial side of the cutout portionof the base member 80, in this particular embodiment, provides betterclearance for the ACL, which is generally located more anteriorly onmedial sides of the ACL attachment region. The more posteriorlypositioned lateral side of connecting portion 82 c also avoidsinterference with the attachment of the posterolateral bundle of the ACLand provides more material on the lateral side for improved strength ofthe asymmetric design. For custom or patient-specific tibial basemembers, the abovementioned angles and other geometric features may bealtered to optimally suit the patient's individual anatomy. Such changesmay be made to satisfy the proper balance between bone conservation andstrength.

In the embodiment shown in FIGS. 30-35 and 47, keel portions 84 a, 84 b,84 c widen or thicken as they approach an intersection with the otherkeel portions. In some embodiments, such as in the embodiment of FIGS.30-35, these blends and transitions of the reinforcing members 88 a, 88b on the sides of the anterior portion 82 c of the base member 80 reducethe stress risers as the top and inside surface portions of the member80 transition to the anterior portion 82 c from the medial 82 a andlateral 82 b sides, where material thickness is limited, so as topreserve minimum tibial insert thicknesses and allow the inserts toslide in and engage looking portions 82 a′, 82 b′ from the anteriorside.

As shown best in FIG. 35, superior-inferior height of the medial 84 aand lateral 84 b keel portions may generally decrease posteriorly toprovide, in some embodiments, an optimized stress distribution andenough flexibility to prevent stress shielding. Moreover, keel portions84 a, 84 b, 84 c are generally angled in an anterior-posterior directionto provide support for medial 82 a and lateral 82 b portions of tibialbase member 80. The angles and positioning of the keel portions 84 a, 84b, 84 c in both anterior-posterior and medial-lateral directions, in atleast some embodiments, provide at least some degree of balance between:(a) supporting the central portion of each side portion 82 a, 82 b ofthe base member 80 during posterior loading of the base member 80; and(b) supporting edge portions of the medial and lateral portions 82 a, 82b of the base member 80 during extreme edge loading at either the medialor lateral side of the base member 80. Moreover, the angles andpositioning of the keel portions 84 a, 84 b, 84 c can be designed tosupport such loads without necessitating a relatively wide anterior keelportion 84 c, which could otherwise interfere with or protrude throughthe anterior cortex of the tibia 220 if made too wide. While theillustrations show the lower edge of the angled side keel portions 84 a,84 b to be a straight edge, the shape of the distal edges may be curvedor stepped in other embodiments such that the depth change of the medialand lateral keel portions 84 a, 84 b is a non-linear function withrespect to posterior distance. Curved or stepped lower edges of sidekeel portion 84 a, 84 b (such as shown in the embodiment of FIG. 7) mayallow better optimization of stress distributions within the tibial basemember 80.

In some embodiments, such as the one illustrated in FIGS. 30-35 and 47,medial and lateral keel portions 84 a, 84 b may have one or morereinforcing, webs 85 a, 85 b connecting peripheral, cement rails 87 a,87 b to the keel portions 84 a, 84 b (FIGS. 34-35). The reinforcementwebs 85 a, 85 b may be strategically located so as to pass under anyhigh stress points, such as at the corners of locking portions 82 a′, 82b′ (FIGS. 32-33), which may be, for example, cutout recesses or pocketslocated on the proximal side of medial 82 a and lateral 84 a portionsand that are configured to receive medial, and lateral, tibial, inserts110, 120 (discussed below). Although not illustrated, webs 85 a, 85 bmay also be provided in the top pocket portions of the locking portions82 a′, 82 b′, so long as inferior sides of the tibial inserts 110, 120are also provided with complementary recesses to afford clearance forthe webs 85 a, 85 b.

As shown in FIG. 34, rounded corners, radiuses, or filets 81 a, 81 b maybe provided between eminence lip portions 89 a, 89 b, 89 c of the tibialbase member so to form the inside surfaces of the cutout portioncontinued to receive the tibial eminence. Said rounded corners,radiuses, or filets 81 a, 81 b may, in some embodiments, reduce thestress risers at those areas thereby overcoming the failures associatedwith the sharp corners typical of prior bi-cruciate retaining designs.The amount of rounding of the corners, in some embodiments, may avoidcausing interference between the implant and the anterior cruciateligament attachment point on the tibia 220.

Moreover, as with other embodiments, heightened walls or eminence lipportions 89 a, 89 b, 89 c along the medial and lateral sides of theeminence cutout area (see, e.g. FIG. 33) may be provided to increase theoverall strength of the base member 80 along inside edges. This addedstrength may facilitate, in at least some embodiments, resistingstresses and other forces on the base member 80 when loaded posteriorly.Moreover, eminence lip portions 89 a, 89 b, 89 c, when combined withundersurface 82 a″, 82 b″, may facilitate the creation of a largerboundary for a cement mantle and allow the cement mantle to grow alongthe base of a prepared tibial eminence. This extra cement along the basecorners and sides of the tibial eminence and between the eminence andbase member 80 may generally improve the resistance to eminencefracture. Heightened walls or eminence lip portions 89 a, 89 b, 89 c mayfurther serve to isolate tibial inserts from both the cement mantle andthe vertical walls of the prepared tibial eminence, and also serve asbuttresses for stabilization of the tibial inserts in the medial-lateraldirection.

The anterior connecting portion 82 c may define a generally trapezoidalsagittal shape, both in sagittal cross section (see, e.g. FIG. 35) andwhen viewed superiorly (see, e.g. FIG. 33). In this embodiment, anteriorportion 82 c is wider (medial-lateral dimension) towards the posterior.Such geometries may, in some embodiments, assist in limiting stressconcentration in the anterior portion 82 c and promote a more evendistribution of stress by encouraging the stresses to flow moreanteriorly to regions where there are fewer stress risers.

In this particular embodiment, the anterior connecting portion 82 c ofthe tibial base member 80 is sloped so as to be thicker(superior-inferior dimension) towards the posterior, which, in someembodiments, may increase strength of the base member 80 proximate theedge of the eminence cutout, while still providing more flexibility onanterior portions of the base member 80 for even stress distributionwhen the base member 80 is loaded posteriorly. For example, if one ofthe medial portion 82 a or lateral portion 82 b is loaded posteriorlymore than the other (e.g., in deep flexion), then torsional forces mayarise in the anterior portion 82 c. In such situations, the flexibilitycreated from a thinner anterior part of the anterior portion 82 c moreevenly distributes torsional stresses, and the thicker posterior portionof the anterior portion 82 c and raised anterior eminence lip 89 cprovides extra strength and rigidity.

FIG. 41 shows the tibial base member 80 with tibial inserts 110 and 120mounted thereon. As shown in FIG. 41, the transition from the thickerlip portion 89 c of the anterior portion 82 c to the more recessedmedial 89 a and lateral 89 b eminence lips provides additional materialat the high stress area at the corners of the eminence cutout portion ofthe base member 80. Therefore, the medial 89 a and lateral 89 b lips canbe shorter than the anterior portion 82 c and the anterior eminence lip89 c without adversely affecting the strength of the tibial base member80. Moreover, reducing the height of the medial 89 a and lateral 89 blips could prevent contact between the tops of the lips 89 a, 89 b andthe femoral component 400, especially in instances where thin polymericinserts 110, 120 are utilized.

Returning to FIGS. 32-33, the upper or proximal side of tibial basemember 80 may include a medial plateau locking portion 82 a′ and alateral plateau locking portion 82 b′ each having a lock detail thatserves to secure a polymeric tibial insert. Such lock details mayinclude, for instance, one or more undercuts, dovetail joints,male-female connections, grooves, ridges, press-fit connections, barbs,latches, pegs, magnets, and other art-recognized connection means. Lockdetails may allow moderate rotational or translational movement of theinserts for mobile bearing applications as will be discussed below.FIGS. 38-46 illustrate tibial base member 80 assembled with medialarticulating insert 110 and lateral articulating insert 120. In someembodiments, the peripheries of the tibial base member 80 and/or tibialinserts 110, 120 align closely with the periphery of the resectedproximal tibia.

While not shown, the upper surfaces of the tibial base member 80 may beconfigured for use with mobile bearings. In other words, the medial andlateral locking portions, in certain embodiments, may be provided with ameans for securing the medial and lateral inserts to the base member,while allowing some finite rotational movement of the inserts. Suchmeans may include, for instance, a male to female connection such as apeg-in-hole configuration or a circular undercut that locks the insertsin 5 degrees of freedom, while still allowing controlled rotation of theinserts relative to the base member. Other means may be provided, suchas tracks and followers, which allow controlled translation of theinserts in any one or more of the anterior-posterior and medial-lateraldirections.

FIGS. 36-37 illustrate a ninth embodiment of a tibial base plate, tibialbase plate 90. As with some of the earlier embodiments described herein,the tibial base plate 90 includes keel portions that are swept back. Inthis particular embodiment, the keel portions 94 a, 94 b, 94 c arestepped to increase bone compression during implant insertion and tocreate zones of increased stress at the corners of the steps. Basemember 90 having stepped keel portions 94 a, 94 b, 94 c may alsoencourage better fixation for both cemented and cementless applications.Instrumentation used to prepare the tibia to receive a tibial basemember may include, in some embodiments, a punch that is or is notstepped to provide more or less interference and press fit engagement.

FIGS. 97-98 illustrate a tenth embodiment of a tibial base plate, tibialbase plate 1700. As with some of the earlier embodiments describedherein, the tibial base plate 1700 includes keel portions that are sweptback. This particular embodiment also includes pegs 1710 or othersuitable structure for providing increased fixation with the preparedtibia 220.

FIGS. 49-52 are front coronal cross-sectional views showing the matinggeometries between tibial base members 80 a-80 d, such base membershaving medial eminence lips 89 a-89 a″ and a lateral eminence lips 89b′-89 b″″, respectively, and a tibial eminence 222 of a prepared tibia220. As shown in the figures, one or both of anterior cruciate ligament(ACL) 310 and posterior cruciate ligament (PCL) 320 are preserved. FIG.53 is a frontal coronal view of a tibial base member 80 assembled withinserts 110, 120 with respect to a prepared tibia 220 and the tibialeminence 222.

In some embodiments, the relative anterior keel portion length and anglecan be optimized based on data collected. It has been found that given amixed anterior keel portion length, increasing the angle of the anteriorkeel portion from vertical generally increases the amount that theanterior keel portion undercuts the anterior tibial eminence, and thattoo much angle can reduce strength of the base member. If too much ofthe anterior keel portion undercuts the eminence, the eminence mass alsobe compromised. Some of the embodiments of the tibial base member wereachieved through a combination of optimizing the shapes to distributestress more efficiently throughout the base member, refining the targetstrength by analyzing previous tibial base member designs which wereknown to fracture, and running computer simulations in an iterativefashion. Input received during cadaver labs was used to identify theamount of and areas for bone removal which were acceptable from ananatomical perspective, and such information was also used to determinethe optimal number, geometries, and orientation of keel portions forincreased strength, and improved initial fixation in variousembodiments. The inventors took into consideration manufacturing thesame tibial base member design from various materials with high and lowfatigue resistance in order to increase the robustness of the designregardless of material strength and properties.

The particular shape of the entire keel selected, combined with theangle of the anterior keel portion, which is in some embodiments isapproximately 70 degrees, essentially creates a “sell-anchoring”feature. In other words, since the anterior keel portion undercuts shecancellous bone (relative to the proximal tibial plateau), it provideshold down forces to counteract pull-out forces.

Also disclosed are methods of unpinning a tibial prosthesis. The methodincludes the steps of determining a resection depth, determining apreferred spatial orientation for the prosthesis, resecting the medialand lateral tibial plateau bone portions without compromising the tibialeminence and ACL/PCL attached thereto, broaching necessary receivingportions for acceptance of one or more fixation features provided on theunderside of the tibial prosthesis, and installing the tibial prosthesisusing cemented or cementless techniques.

2. Tibial Inserts

The above described and other embodiments provide improved tibialinserts, such as medial insert 110 and lateral invert 120 illustrated inFIGS. 38-44 as assembled with base member 80. In some embodiments,medial insert 110 is thinner than the lateral insert 120 so as to matchthe varus joint line present on a femoral component. In someembodiments, for instance, the lateral insert 120 may be approximately2.5 mm. thicker than the medial insert 120, in order to create a3.degree. varus joint line that matches a 3.degree. varus joint line ofthe femoral component. The tibial articular geometry of some embodimentsgenerally includes a concave medial portion on the medial insert 110 anda convex lateral portion on the lateral insert 120. A coronal conformitymay be present on inner portions of one or both of the inserts 110, 120.This coronal conformity, for instance, may comprise a mesial lip, which,as described further below, may vary in height along theanterior-posterior direction.

FIGS. 54-58 show various views of an embodiment of a lateral insert 120,while FIGS. 59-63 show various views of an embodiment of a medial insert110.

The lateral insert 120 of FIGS. 54-58 defines a superior articulationsurface, defining several different contours in various planes. FIGS. 57and 58 are cross sections of the lateral insert 120 in certain coronal(FIG. 57) and sagittal (FIG. 58) planes. FIG. 57 illustrates a contour126 a defined by a relatives anterior, coronal cross section of lateralinsert 120. FIG. 58 illustrates a contour 124 b defined by a relativelymiddle, sagittal cross section of lateral insert 120. FIGS. 90a-c are aseries of sagittal cross sections of an embodiment of a left, lateralinsert illustrating the contours of that insert from relatively mesial(e.g. FIG. 90a ) to relatively outer (e.g. FIG. 90e ) portions of theinsert. FIGS. 91a-k are a series of coronal cross sections of the sameembodiment as shown in FIGS. 90a-e , the coronal cross sections of FIGS.91a-k progressing from relatively anterior portions (e.g. FIG. 91a ) torelatively posterior portions (e.g. FIG. 91k ) of the insert.

As shown in the embodiments of FIGS. 54-58 and 90-91, and as describedin further detail below, lateral insert 120 defines a mesial lip 128 anda circumferential chamfer 129. In some embodiments, at least some partsof the anterior portions and contours of the lateral insert 120 arerelatively more conforming to a femoral condylar surface than otherportions of the insert 120. As shown in FIG. 56, lateral insert 120 mayalso include peripheral steps 127 a, 127 b. FIGS. 56 and 58 illustrateslock mechanism 122 used to secure lateral insert 120 to the tibial basemember.

As shown in the embodiments of FIGS. 54-58 and 90-91, mesial lip 128 israised relative to other portions and contours of the insert 120. Asshown in FIG. 58, illustrating a sagittal cross section of the insert120, such cross section taken through a middle portion of the insert120, the raised mesial lip 128 extends from anterior to posteriorportions of the insert 120. Mesial lip 128, in some embodiments,provides resistance to lateral femoral translation and preventsimpingement between the femoral component 400 and the tibial eminence222. The height of the mesial lip can be selected to provide a desiredlevel of resistance, with a greater height providing more resistance. Asshown in these embodiments, the height of the mesial lip relative toother portions of the insert 120 gradually decreases as it extends in ananterior to posterior direction. In the embodiments of FIGS. 54-58 and90-91, outer side portions (near chamfer 129) of the lateral insert 120are substantially flat and have little to no coronal conformity with thefemoral condylar articulation surfaces. In some embodiment, the maximumheight of the mesial lip 128 is between a range of approximately 0.025inches and approximately 0.125 inches relative to the substantially flatouter side portions. In some embodiments, the maximum height of themesial lip 128 is between approximately 0.035 inches and approximately0.065 inches for the lateral insert 120.

FIGS. 59-63 illustrate an embodiment of a medial insert 110, whichdefines a Superior articulation surface, defining several differentcontours in various planes. For instance, FIG. 62 shows a coronal crosssection of the medial insert 110 taken, at a relatively middle portionof the insert 110, showing coronal contour 116 a. FIG. 63 shows asagittal cross section of the medial insert 110 taken at a relativelymiddle portion of the insert, showing contour 114 b. FIGS. 92a-c are aseries of sagittal cross sections of an embodiment of a left, medialinsert illustrating the contours of that insert from relatively mesial(e.g. FIG. 92a ) to relatively outer (e.g. FIG. 92c ) portions of theinsert. FIGS. 93a-m are a series of coronal cross sections of the sameembodiment as shown in FIGS. 92a-e , the coronal cross sections of FIGS.93a-m progressing from relatively anterior portions (e.g. FIG. 93a ) torelatively posterior portions (e.g. FIG. 93m ) of the insert.

Like the lateral insert, medial insert 110 also includes a mesial lip118 and a circumferential chamfer 119 (e.g. FIG. 60). In someembodiments, anterior, mesial portions of the insert 110 are moreconforming to an associated femoral component than other portions of theinsert. As shown in FIG. 60, medial insert 110 also includes peripheralsteps 117 a, 117 b. FIGS. 61 and 63 illustrate a lock mechanism 112 usedto secure medial insert 110 to the tibial base member.

As shown in FIGS. 62-63 and 92-93, mesial lip 118 is raised relative toother portions and contours of the insert 120. As shown in FIG. 63,illustrating a sagittal cross section of the insert 110, such crosssection taken through a middle portion of the insert 110, the raisedmesial lip 118 extends from anterior to posterior portions of the insert110. Mesial lip 118, in some embodiments, provides resistance to lateralfemoral translation and prevents impingement between the femoralcomponent 400 and the tibial eminence 222. The height of the mesial lipcan be selected to provide a desired level of resistance, with a greaterheight providing more resistance. As shown, in these embodiments, theheight of the mesial lip relative to other portions of the insert 110gradually decreases as it extends in an anterior to posterior direction.In the embodiments of FIGS. 62-63 and 92-93, outer side portions (nearchamfer 119) of the medial insert 110 are substantially flat and havelittle to no coronal conformity with the femoral condylar articulationsurfaces. In some embodiments, the maximum height of the mesial lip 118is between a range of approximately 0.025 inches and approximately 0.125inches relative to the substantially flat outer side portions. In someembodiments, the maximum height of the mesial lip 118 is betweenapproximately 0.035 inches and approximately 0.064 inches for the medialinsert 118.

FIGS. 64-67 illustrate graphically and pictorially the kinematics of themedial and lateral inserts 110, 120 of FIGS. 54-63 when used with othercomponents, such as a femoral component 400 and patellar component 600in certain arthroplasty procedures. Using LifeMOD™ computer simulations,the inventors have determined that providing a mesial lip 118 on themedial tibial insert 110 serves to prevent the femoral component 400from translating laterally in response to the lateral forces applied tothe femoral component 400 by the patella due to the quadriceps angle, or“Q-angle.” In some embodiments, without the mesial lip 118, the femoralcomponent 400 may translate laterally in flexion due to patella shear,creating an environment where the medial condyle 408 moves too close tothe attachment point of the posterior cruciate ligament 320 andsurrounding bone 220, 222. In addition to increasing the overallperformance of the prosthesis over prior art designs, in someembodiments, the raised mesial lip 118 further provides additionaltibio-femoral contact when the leg is in extension. In some embodiments,it is envisaged that the medial insert 110 comprises a mesial lip 118and the lateral insert 120 does not comprise a mesial lip 128, althoughmesial lips 118, 128 may be added to both inserts 110, 120 foradditional stabilization.

FIGS. 64-66 graphically illustrate the medial femoral rollback, lateralfemoral rollback, and external femoral rotation respectively of femoralimplant 400 when used in conjunction with the implant 100 shown in theembodiment of FIGS. 38-46. This, in some embodiments, may be in contrastto at least some previous bicruciate-retaining designs, which employedoverly-conforming coronal profiles in regions adjacent to the femoralcomponent towards the midline and outer peripheral edges of the tibialinsert. This over-conformity present in some prior art designsnegatively constrains internal-external rotation of the femoralcomponent and reduces or eliminates medial-lateral translation. At leastsome known designs have also demonstrated high amounts of conformity atanterior and posterior portions of the insert, which negatively limitfemoral rotation during knee extension and flexion. The design shown inFIG. 68, in this particular embodiment, generally only provides coronalconformity towards a midline of the tibia, said coronal conformitygradually reducing towards the posterior edges of the insert. Because ofthis reduction in conformity, this particular design more freely allowsinternal and external rotation of the femoral component 400 and moreclosely replicates normal knee kinematics in flexion, where the femoralcomponent 400 is rotated externally relative to the tibial prosthesis100. Other embodiments, however, may feature relatively highlyconforming inserts similar to those of other prior art designs.

In some instances, a plurality of different posterior slope angleoptions may be provided to tibial inserts 110 and/or 120. In oneembodiment, inserts such as 110 and/or 120 are thinned posteriorly bydifferent amounts so as to effectively rotate the articular surfaces bya flexion-extension angle relative to the bottom surfaces of the inserts110, 120 and provide more posterior slope. Such an option may, in someembodiments, allow a surgeon to selectively adjust joint laxity when theknee is in flexion. For instance, several pairs of medial 110 andlateral 120 inserts may be provided, each pair differing in posteriorslope from the other pairs by a specified number of degrees betweenabout 1-4 degrees, for instance 2 degrees. Other options may includepairing medial 110 and lateral 120 inserts, wherein the posterior slopeof the medial insert 110 differs from the posterior slope of the lateralinsert 120. Such options may generally allow the flexion space to beadjusted without necessarily requiring a re-cut of tibial bone 220.Multiple dullness options for each of the medial 110 and lateral 120inserts are also provided for the abovementioned options to affordproper ligament balance. Various combinations and configurations ofinsert thicknesses, medial-lateral slope, and anterior-posterior slopemay be utilized to suit the particular anatomical needs of an individualpatient. The options of multiple thickness, medial-lateral slope, andanterior-posterior slope may also be configured in the tibial base plateto provide these configurations while using a single insert.

In some embodiments, the articular geometries of the medial 110 andlateral 120 inserts may be provided by a single cruciate-containinginsert 500, which, as shown in FIGS. 69, 71, 73, 75, 78, and 80,comprises concave medial and lateral articulating surfaces. As shown inFIG. 80, the lateral portion 510 of the insert 500 may be thicker (insome embodiments, approximately 2.5 mm thicker) than the medial portionto allow functionality with the femoral components 400 shown. Thethicker lateral portion 510, in this particular embodiment serves tomatch the varus joint line present on the femoral component 400.

In other embodiments, medial 110 and lateral 120 inserts may beprovided, each having different posterior slope angles or thicknesses,and may be utilized in various combinations in order to addressdifferent medial and lateral collateral ligament balancing needs. Insome instances, a set of inserts 110, 120 including a plurality of sizesmay be provided in a surgical implant kit, wherein a general anglebetween a bottom plane of a particular insert 110, 120 and itscorresponding articulating surface varies between inserts. This anglemay increase or decrease in either or both, of an anterior-posteriordirection and a medial-lateral direction independently or collectively.Providing multiple posterior slope options may advantageously reduce theneed for re-cutting the tibia 220.

FIGS. 56 and 68 illustrates an example of a convex lateral insert 120,which facilitates external rotation of the femoral component 400 duringflexion and through lateral femoral rollback, while the medial femoralcondyle 408 is constrained by the sagittal concave geometry of themedial insert 110 as provided by some embodiments.

As another alternate to using separate tibial inserts 110, 120, a tibialbase member 1500 shown in FIG. 88 may comprise integrally-formedmonolithic articulating surfaces. Other embodiments, such as shown inFIG. 89, may include a tibial prosthesis 1600 formed of a porousstructure material 1602 such as a metal foam, with articulating surfaces1604 modularly or integrally provided at a proximal region of the porousstructure 1602, as shown in FIG. 89. For instance, the articulatingsurfaces 160-1 may be formed as a solid metal, ceramic, polymer,coating, or compliant material disposed on a proximal side of the porousstructure. This may be accomplished using conventional rapidmanufacturing techniques such as selective laser sintering (SLS),electron beam welding (EBM), 3D printing, or stereolithography.Alternatively, the porous structure 1602 may be overmoulded with apolymer to form a monolithic base member 1600 having a porous structure1602 and an articulating surface 1604 of different materials.

3. Femoral Components

Also provided are improved femoral components. For example, the femoralcomponent 400 shown in FIGS. 67-75 includes a medial condyle and alateral posterior condyle 400 that comprises a posterolateral chamfer404 (see, e.g. FIGS. 68-69, 72-74). As shown in FIGS. 74-75. In someembodiments, posterolateral chamfer 404 has a depth or distance d ofbetween approximately 1 and approximately 5 mm, and more preferablybetween approximately 2 and approximately 4 mm, for exampleapproximately 2.8 mm, and an angle Φ between approximately zero andapproximately 25 degrees, and more preferably between approximately 5and approximately 15 degrees, for example approximately 10 degrees, tocreate a clearance with the posterior lateral tissue such as thepopliteal tendon in deep knee flexion. The chamfer 404 may originate adistance D from a proximal bone engaging surface configured to mate witha distal femoral bone cut, said distance D, for example, being betweenapproximately 3 and approximately 20 mm, and more preferably betweenapproximately 8 and approximately 15 mm, for example, approximately 11mm. Distances d and D may increase proportionally or disproportionallywith increasing femoral component 400 sizes. In some embodiments, forexample, larger sizes of femoral component 400 may employ an angle Φ ofapproximately 10.degree. and a distance D of approximately 11 mm,whereas smaller sizes of femoral, component 400 may employ a smallerdistance D of approximately 10 mm.

Similarly, medial posterior condyle 408 may compose on its inner surfacea posterolateral chamfer 410, shown in FIGS. 74, 76, 79-81, having anangle ψ between approximately 0 and approximately 10 degrees and morepreferably between approximately 3 and approximately 7 degrees, forexample approximately 5 degrees as shown in FIG. 74. Such a chamfer maybe combined with another chamfer 470 that may be swept around an innersagittal radius of posterior medial condyle 408 to provide additionalclearance with the tibial eminence 222 and posterior cruciate ligament320, without decreasing bone coverage. In some embodiments, theposterolateral chamfer 470 starts just posterior to patella contactingareas of the femoral component 400, and therefore, it may not sweeparound intercondylar patellar contacting regions 412 of the femoralcomponent. Rather, posterolateral chamfer 470 may be more pronounced inposterior portions of the medial femoral condyle 408. Top edges of thetibial eminence 222 may also be chamfered using a rongeur to furtheravoid impingement with the femoral component 400.

FIG. 94 is a medial sagittal view of a medial condyle 455 of a femoralcomponent 450 according to one aspect. The medial posterior condyle 455may comprise on its inner surface a posterolateral chamfer 470. FIGS.95a-95b are various coronal cross sectional views taken along the linesA-A through K-K, respectively, of FIG. 94 illustrating posterolateralchamfer 470. As shown in FIGS. 95a-95k , femoral component includes arounded edge 460 when viewed along lines A-A, J-J- and K-K, and includesa posterolateral chamfer 470 when viewed along lines B-B, C-C, D-D, E-E,F-F, G-G, H-H, I-I. The angle ψ of posterolateral chamfer 470 is betweenapproximately 15 and approximately 40 degrees in some embodiments.

As shown in FIG. 68, the anterior flange of the femoral component 400may comprise an anterolateral chamfer 402 on lateral and/or medial sidesto reduce tension on the retinaculum tissue, which may be common withsome prior art femoral designs.

Various modifications could be made to the exemplary embodiments, asdescribed above with reference to the corresponding illustrations,without departing from, the scope of the invention, and therefore, it isintended that all matter contained in the foregoing description andshown in the accompanying drawings shall be interpreted as illustrativerather than limiting. For example, the novel features of the tibialinserts disclosed may be readily applied to instrumentation such astibial insert trials, as well as implants designed to be implanted.Thus, the breadth and scope of the invention should not be limited byany of the above-described exemplary embodiments, but should be insteaddefined only in accordance with any claims which may be appended heretoand their equivalents.

1. A tibial prosthesis, comprising: an insert with a tibial articulationsurface for articulation with a femoral condylar articulation surface,the tibial articulation surface comprising: an anterior-mesial portion,the anterior-mesial portion curved to conform to the femoral condylararticulation surface; and a mesial lip extending in an anterior toposterior direction along a mesial edge of the articulation surface,wherein a height of the mesial lip at the extent of the mesial lip inthe anterior direction is greater than a height of a central portion ofthe tibial articulation surface.
 2. The tibial prosthesis of claim 1,wherein a height along the mesial lip decreases in the anterior toposterior direction.
 3. The tibial prosthesis of claim 1, wherein thetibial articulation surface comprises a flat portion and the flatportion includes at least part of the central portion.
 4. The tibialprosthesis of claim 3, wherein the flat portion includes at least partof a lateral portion of the tibial articulation surface.
 5. The tibialprosthesis of claim 3, wherein the flat portion is at the height of thecentral portion.
 6. The tibial prosthesis of claim 1, wherein the tibialarticulation surface comprises a curved surface connecting the mesialedge to a flat surface of the central portion.
 7. The tibial prosthesisof claim 1, wherein the tibial articulation surface defines a pluralityof contours in a plurality of planes.
 8. The tibial prosthesis of claim1, comprising a chamfer extending circumferentially around the tibialarticulation surface.
 9. The tibial prosthesis of claim 1, wherein aposterior-outer portion of the tibial articulation surface issubstantially flat.
 10. The tibial prosthesis of claim 1, wherein theheight of the mesial lip at the extent of the mesial lip in the anteriordirection is between 0.025 inches and 0.125 inches greater than theheight of the central portion of the tibial articulation surface
 11. Thetibial prosthesis of claim 1, comprising a locking mechanism to securethe insert to a tibial base member.
 12. An insert for a tibialprosthesis, comprising: a tibial articulation surface for articulationwith a femoral condylar articulation surface, the tibial articulationsurface comprising: an anterior-mesial portion, the anterior-mesialportion curved to conform to the femoral condylar articulation surface,and a mesial lip extending in an anterior to posterior direction along amesial edge of the articulation surface, wherein a height of the mesiallip at the extent of the mesial lip in the anterior direction is greaterthan a height of a central portion of the tibial articulation surface;and a chamfer extending circumferentially around the tibial articulationsurface.
 13. The insert of claim 12, wherein a height along the mesiallip decreases in the anterior to posterior direction.
 14. The insert ofclaim 12, wherein a posterior-outer portion of the tibial articulationsurface is substantially flat.
 15. The insert of claim 12, wherein thetibial articulation surface comprises a flat portion and the flatportion includes at least part of the central portion.
 16. The insert ofclaim 15, wherein the flat portion includes at least part of a lateralportion of the tibial articulation surface.
 17. The insert of claim 15,wherein the flat portion is at the height of the central portion. 18.The insert of claim 12, wherein the tibial articulation surfacecomprises a curved surface connecting the mesial edge to a flat surfaceof the central portion.
 19. The insert of claim 12, wherein the tibialarticulation surface defines a plurality of contours in a plurality ofplanes.
 20. The insert of claim 12, comprising a locking mechanism tosecure the insert to a tibial base member.